Overview of Chengdu plain

Chengdu Plain is located between Longquan Mountain Range, Longmenshan Mountain Range and Qionglai Mountain Range, with flat terrain, convenient irrigation and drainage, mild climate and fertile soil. It is an important commodity grain producing area in China.

Chengdu Plain, also known as West Sichuan Plain, is called western sichuan bazi (Sichuan Dialect Pinyin: Cuanxi Bazi) in Sichuan dialect. It is an alluvial plain located in the west of Sichuan Basin in China and the largest plain in the southwest of China.

Chengdu Plain is one of the largest plains and dense river networks in southwest China, and the largest mirabilite producing area in China, also known as Penxiping Plain or Chuanxi Plain, is located in the west of Sichuan Basin. Chengdu Plain in a broad sense lies between Longquan Mountain, Longmen Mountain and Qionglai Mountain, and reaches Leshan Wu Tong Bridge in the south. The central part is the Minjiang River and Tuojiang River alluvial plain, and the southern part is the Qingyi River and Dadu River alluvial plain. There are hills and plateaus between the three plains, with a total area of 23,000 square kilometers. In a narrow sense, Chengdu Plain only refers to the Minjiang River and Tuojiang River alluvial plains bounded by guanxian, Mianzhu, Luojiang, Jintang, Xinjin and Qionglai, covering an area of 8,000 square kilometers, which is the main part of the western basin plain. Because Chengdu is located in the plain, it is also called Chengdu Plain. Chengdu Plain in a broad sense is located between Longquan Mountain Range, Longmenshan Mountain Range and Qionglai Mountain Range, with a total area of about 22,900 square kilometers, including 23 counties (cities, districts) in Chengdu except Jintang County, Pujiang County and Longquanyi District, and wutongqiao district in Leshan City in the south, covering many counties (cities, districts).

Jingyang District, Guanghan City, shifang city City and Mianzhu City of Deyang City;

Leshan City Central District, wutongqiao district, Jiajiang County;

Dongpo District and Pengshan District of Meishan City.

In a narrow sense, Chengdu Plain only refers to the impact fan-shaped plain of Minjiang River and Tuojiang River with Dujiangyan as the apex and Chengdu as the center.

Geographical definition

Chengdu Plain (called western sichuan bazi and Tianfu Plain in Sichuan dialect) and Panxi Plain are alluvial plains located in the central and western Sichuan Basin in China, the largest plain in the southwest of China, the largest plain in Sichuan and one of the areas with dense river networks. In a broad sense, Chengdu Plain is between Longquan Mountain, Longmen Mountain and Qionglai Mountain, south to Leshan Wu Tong Bridge, middle to Minjiang River and Tuojiang River alluvial plain, south to Qingyi River and south to Dadu River. The three plains have hills and plateaus, covering many counties (cities, districts) with a total area of 23,000 square kilometers. In a narrow sense, the West Sichuan Plain only refers to the Minjiang River and Tuojiang River alluvial plains bounded by Dujiangyan, Mianzhu, Luojiang, Jintang, Xinjin and Qionglai. It is about 265,438+00 kilometers long and 50,000-70,000 wide, which is the main part of the western Sichuan Plain. Because Chengdu is located in the middle of the plain, it is called Chengdu Plain. According to the calculation of not less than 600 people per square kilometer, the population of Chengdu Plain is about 7 million, while the population of Chengdu is more than 6.5438+million.

Chengdu Plain in a broad sense is located between Longquan Mountain Range, Longmen Mountain Range and Qionglai Mountain Range, with a total area of 22,900 square kilometers, including: except Jintang County, Pujiang County, Shuangliu County and Longquanyi District in Chengdu; Jingyang District, Guanghan City, shifang city City and Mianzhu City of Deyang City; Leshan City Central District, wutongqiao district, Jiajiang County; Dongpo District, Meishan City, pengshan county. guide

The narrow sense of Chengdu Plain only refers to the impact fan-shaped plain of Minjiang River and Tuojiang River with Dujiangyan as the apex and Chengdu as the center, and it is also the main part of the broad sense of Chengdu Plain.

geological structure

Beichuan-Wenchuan-Kangding-Xiaojin River is bounded by the Yangtze Platform in the east and the Songpan-Ganzi geosyncline in the west. Although the Chengdu Plain is adjacent to the Longmenshan fault zone, it belongs to the Yangtze Platform with very stable geology (that is, the South China Block). Sichuan Basin entered a stable platform development period from the end of Jurassic-Cretaceous Himalayan tectonic activity (about 65.438+0.3 billion years ago), during which Longmen Mountain was formed in Mesozoic and early Cenozoic (about 65 million years ago).

About 2 million years ago, a new intense crustal movement occurred in Cenozoic Tertiary, forming Qingcheng Mountain Range, which was the last orogenic movement closest to Chengdu Plain, but there was no major geological tectonic activity in Chengdu Plain itself. After the western mountainous areas were uplifted successively, Sichuan Basin, as the Longmenshan foreland depression, was filled with a set of Mesozoic continental clastic deposits, of which the highest sedimentary thickness in Chengdu Plain was 8000 ~ 10500m, which proved its long and stable geological history from one side.

Except for the western fault zone, the geology in the south and east of Chengdu Plain is relatively stable. The Pujiang-Xinjin fault zone in the southwest of Chengdu Plain is about 80 kilometers long and small in scale. There have been two earthquakes of magnitude 5 or so in this fault zone, and the tectonic activity is not obvious. The Longquanshan fold and fracture zone in the east of Chengdu Plain has a fracture scale of about 90 kilometers. In the past 2 million years, there has been no obvious geological activity, and it has been eroded into platforms and shallow hills by wind and rain.

Chengdu Plain has loose surface and thick sediments. The thickness of sediment in the central area of the plain is 300 meters. Quaternary sediments are covered with silt and clay. It has a good structure and is suitable for farming. It is the most fertile soil (purple soil) in Sichuan Province. It is 450 ~ 750m above sea level, with a flat terrain and a slight inclination from northwest to southeast, with an average gradient of only 3. 1 ‰ ~ 10.3.

Geological composition

The geological structure of Chengdu Plain is covered with a thick layer of muddy sediments, which are distributed on very hard rocks. According to the deep geophysical data in Sichuan, the basement of the basin is the crystalline basement of early Precambrian granite with high degree of hardening, and the strata in Chengdu Plain are very hard. It is miscellaneous fill with an average depth of about 5 ~ 7m, and it is sandy pebble with an average depth of about 7.11~10.24m. Because the miscellaneous fill and sandy pebble are "soft" and have many small gaps between them, they have a strong ability to consume seismic waves and can well protect the buildings they bear. Although there are many faults in the west, the energy of crustal movement is often released on the faults. The earthquake resistance of hard rocks and the buffering effect of soil can significantly reduce the damage of earthquakes. Therefore, although Chengdu is close to the earthquake-prone zone, there is no record of earthquake damage in history.

Geological protection

At the "Chengdu Plain Wetland Protection and Sustainable Utilization Forum" held on 20 1 1, Shen You, chairman of Chengdu Bird Watching Society, expressed regret that Chengdu Plain Wetland was being disturbed by human activities. The investigation report shows that there is no natural wetland in the strict sense below the altitude of 1000 meters in Chengdu Plain. Yin (Professor, School of Geology, Chengdu University of Technology): In history, Chengdu used to be an area with dense wetlands and developed river networks, but at present, the disappearance of wetlands in Chengdu is closely related to unreasonable economic activities of human beings. With the increase of population and economic development, many natural wetlands have become farmland and other land, so people should pay attention to the disappearance of natural wetlands. Geological landscape

Many tourist attractions have been born in the fertile soil of western Sichuan plain. For example, Hailuogou, located at the foot of Gongga Snow Mountain, the highest peak in Sichuan, is a millennium glacier. Places with many natural hot springs are very suitable for leisure and vacation, and at the same time, you can appreciate the unique ethnic customs of ethnic minorities, which is very beautiful and spectacular. Topographic features Sichuan plain has a good terrain, and the temperature is higher than other areas at the same latitude. The maximum Leng Yue average temperature is 8℃ ~ 10℃. The soil is mainly purple soil, which is rich in various minerals. Agriculture in this area is relatively developed. Later, due to the long-term cultivation of rice, some soil became paddy soil.

She has the richest vast plain in the west, located between Longquan Mountain and Longmen Mountain.

Between Qionglai Mountain, it starts from Leshan in the north and reaches Wu Tong Bridge in Leshan in the south, with a total area of about 2,2901km2. The Dujiang weir built in Qin Dynasty cared for her like a giant hand, and Siguniang Mountain was its strong backbone. It has fertile and flat green plains and thousands of years of time and space inheritance.

river

Rivers on the plain include Tuojiang River which flows through Pengzhou, Guanghan and Jintang. Minjiang River flows through Dujiangyan and Xinjin; From Dujiangyan via Wenjiang District to Wuhou District to Huayang Jiang 'an River; Improve the internal water diversion from Dujiangyan to Qingshui River in Chengdu via Pixian County; The boundless river from Dujiangyan to Qingbaijiang via Pengzhou; Starting from Dujiangyan, it flows into Chengdu Jinjiang via Sandaoyan in Pixian County and jinniu district. Many rivers in Chengdu Plain can be traced back to Minjiang River in Dujiangyan. Shahe River and Funan River are tributaries of Jinjiang, and Qingshui River flows into Jinjiang. Jinjiang and Jiang 'an River meet in Huayang to form Fuhe River, which is reinjected into Pengshan Minjiang River.

Climatic conditions

Chengdu Plain belongs to subtropical monsoon climate (moderate and humid climate in the middle subtropical zone), with purple soil as the main soil, mainly planting rice and cotton. Under the irrigation of Minjiang River and other rivers below Dujiangyan, the subtropical humid monsoon climate makes the average annual temperature in Chengdu Plain about 65,438 06℃, the average annual precipitation about 65,438 0,000 mm, and the average annual rainy days about 300 days. The foggy weather is one of the rainy areas in China. However, because the plain is adjacent to the western Sichuan Plateau, it is deeply affected by the sinking of cold air in mountainous areas, and most of the river water in the plain comes from the melting water of snow and ice in the western plateau and mountainous areas. At the same time, in the low-lying ancient river area on the plain, the groundwater level is high and the soil is cold and wet. Therefore, the air temperature, water temperature and ground temperature in Chengdu Plain are low, and the thermal conditions are slightly worse than those in other areas of Sichuan Basin.

Spring in Chengdu Plain comes very early and usually blooms around the Lantern Festival. In March and April, rape blossoms were in full bloom on the Chengdu Plain, and the fields turned into golden oceans everywhere. In summer, Chengdu is much cooler than other places at the same latitude. Especially in July, Chengdu is located at the periphery of the western edge of the subtropical high, which is influenced by the southwest monsoon from the Indian Ocean. The rainstorm is concentrated, and the daily average temperature is maintained at around 25℃. It is an ideal summer resort for people in eastern and southern Sichuan. Like spring, autumn in Chengdu Plain comes very early. In early September, it joined the embrace of autumn girls in Beijing, Xi and other cities. But at this time, the autumn rain in West China will last for half a month, and the sky is gloomy and sad. In winter, the Chengdu Plain is sometimes clear in Wan Li, and sometimes the wind is cold. The average snowfall is 3-5 days, and the number of snow days is 1 day. 1 1 late month1early February is mostly sunny, and the temperature can reach 10℃ in the afternoon. However, due to the high altitude and strong clear-sky radiation in Chengdu Plain adjacent to the western Sichuan Plateau, the minimum temperature in sunny nights often drops below freezing point, and sometimes even drops to -5℃. 1 late February and1month are mainly rainy and snowy weather. The highest temperature is generally less than 10℃, and sometimes even hovers at 5℃. Due to the thick insulation effect of clouds, the minimum temperature will generally rise to about 2℃, but rainy and snowy weather generally gives people a wet and cold feeling. In ancient times, people from the West Sea went to the emperor to borrow land, but the emperor refused to borrow it, so people had to find their own way. People saw that the Emperor of Heaven only cared about dozing off, so they cut down some pine and cypress branches to burn. When the fire lit up, plumes of smoke curled up, making the Emperor feel fragrant and comfortable. People are busy adding pine branches and cypresses. At that time, cigarettes filled the air, and the world slept more deeply.

When everyone saw that the Emperor of Heaven was asleep, they quickly picked up the sacred soil from the table and ran away. This run woke the Emperor of Heaven. Seeing someone running out of the Heavenly Palace and boarding a ship, he shouted, "Tomorrow at the fifth watch, we must recapture the holy land."

People listened to the instructions of the Emperor of Heaven and returned to the West Sea. Everyone picked up the sacred soil and threw it into the sea. Strangely, the sea surface in the West Sea was originally a turbulent wave, and the tsunami shook the sky. The land dispersed into the sea, and immediately it was calm, and the land was exposed to the water. People took sacred soil, abandoned the ship and went ashore, running and scattering, forcing the sea to go backwards. When the last soil was scattered, the west sea did not even turn over the flowers, and it completely became land. When people look back again, they can't see the flat dam on the side, which is smooth, flat, black and oily. Everyone is ecstatic, some are running on the ground, some are rolling on the ground. When we are happy enough, everyone is busy planting rice, mulberry and sericulture. The sun went down and a night watch banger rang. Everyone remembered that the Emperor of Heaven had called for the five tables to be returned to the soil, and they all shed tears when they touched the newly reclaimed land under their feet.

People who work at night are also very anxious and don't know what to do. Knock the second watch, the third watch, and the fourth watch. He thought that as soon as the morning star rises and the night watchman rings, the land will be gone and he will suffer on the ship again. So he threw away the bangzi and went back to sleep. Since then, people in Chengdu Plain have never heard of playing the fifth watch for generations. The Heavenly Emperor pricked up his ears to listen to the five-watch gong on earth. As soon as the fifth watch rings, he will take back the holy land. Listen, listen, my ears are hanging on my shoulders, but the gong of Chengdu bazi is silent at five o'clock. Until today, the soil of Chengdu bazi is intoxicating oily black. It turned out to be the soil of God and the incense ashes of pine and cypress branches. Plug in a pole, it will grow into useful materials, and everything planted will have a good harvest, so it is called "the land of abundance".